如何在不带空格的makefile中的行间打断字符串? [英] How to break a string across lines in a makefile without spaces?

问题描述

在makefile中，使用\转义换行符可以在多个源代码行之间拆分单行长字符串内容.但是，换行符替换为空格.源中是否存在不影响字符串内容的透明换行符?

In a makefile, escaping a new-line with \ allows to split a single-line long string content across multiple source lines. However, the new-line is replaced with a space. Is there a transparent line break in the source that does not affect the string content?

VAR=w\
o\
r\
d

all:
    echo $(VAR)

所需的输出是'word'，但实际的输出是'w o r d'.

The desired output is 'word', but the actual output is 'w o r d'.

推荐答案

最简单的解决方案是使用$\<newline>拆分 行(至少在使用GNU Make的情况下):

The simplest solution is to use $\<newline> to split the line (at least if you are using GNU Make):

VAR = w$\
      o$\
      r$\
      d

all:
    echo $(VAR)

输出将是没有空格的单词".这是因为GNU Make将用单个替换backslash-newline-whitespace 空格，使对VAR的赋值等效于:

The output will be "word" with no spaces. This is because GNU Make will replace backslash-newline-whitespace with a single space, making the assignment to VAR be equivalent to:

VAR = w$ o$ r$ d

来自 https://www.gnu.org/software/make/manual/html_node/Reference.html#Reference : 美元符号后跟一个非美元符号的字符， 开括号或开括号将单个字符视为 变量名称."因此，$<space>对是的扩展 名称为单个空格字符的变量.从此 变量默认情况下未定义，它将扩展为空 字符串.

From https://www.gnu.org/software/make/manual/html_node/Reference.html#Reference: "A dollar sign followed by a character other than a dollar sign, open-parenthesis or open-brace treats that single character as the variable name." So the $<space> pairs are expansions of the variable whose name is a single space character. Since this variable is not defined by default, it will expand to the empty string.

请注意，变量VAR仍将包含 $<space>配对直到扩展.大多数时候，这 没关系，但是如果您的makefile依赖于使用 $(value VAR)处理基础(未扩展)值， 上述技术可能会提供令人惊讶的结果.

Note that the variable VAR will still contain the $<space> pairs until it is expanded. Most of the time, this doesn't matter, but if your makefile depends on using $(value VAR) to process the underlying (unexpanded) value, the above technique may provide surprising results.

此外，最近发布的GNU Make 4.3现在明确记录了这一点. 分割线的技术( https://www.gnu.org /software/make/manual/make.html#Splitting-Lines ):

Also, the recently released GNU Make 4.3 now explicitly documents this technique for splitting lines (https://www.gnu.org/software/make/manual/make.html#Splitting-Lines):

在不添加空格的情况下进行拆分

Splitting Without Adding Whitespace

如果您需要分割一行，但又不想添加任何空格，则可以利用一个巧妙的技巧:用三个字符美元符号/反斜杠/换行符替换反斜杠/换行符对:

If you need to split a line but do not want any whitespace added, you can utilize a subtle trick: replace your backslash/newline pairs with the three characters dollar sign/backslash/newline:

var := one$\
       word

make删除反斜杠/换行符并将以下行压缩为一个空格后，等效于:

After make removes the backslash/newline and condenses the following line into a single space, this is equivalent to:

var := one$ word

然后make将执行变量扩展.变量引用"$"指的是一个不存在一个字符名称"(空格)的变量，因此扩展为空字符串，并给出与以下内容等效的最终赋值:

Then make will perform variable expansion. The variable reference ‘$ ’ refers to a variable with the one-character name " " (space) which does not exist, and so expands to the empty string, giving a final assignment which is the equivalent of:

var := oneword

有关其他想法，请在此处查看我对类似问题的回答: 如何在不带空格的Makefile中跨多行破坏变量定义?

For other ideas, see my answer to a similar question here: How can I break a variable definition across multiple lines in a Makefile without spaces?

可以在以下位置找到对行连续选项的更长时间的处理 我的文章"GNU使行继续": http://drmikehenry.com/gnu-make-line-continuations/

A longer treatment of line continuation options can be found in my article "GNU Make line continuations": http://drmikehenry.com/gnu-make-line-continuations/

这篇关于如何在不带空格的makefile中的行间打断字符串?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！